Field
This disclosure relates generally to mole or gas delivery devices, and more particularly, to a method of and system for pulse gas delivery. As used herein the term “gas” includes the term “vapor(s)” should the two terms be considered different.
Overview
The manufacture or fabrication of semiconductor devices often requires the careful synchronization and precisely measured delivery of as many as a dozen gases to a process tool. For purposes herein, the term “process tool” may or may not include a process chamber. Various recipes are used in the manufacturing process, involving many discrete process steps, where a semiconductor device is typically cleaned, polished, oxidized, masked, etched, doped, metalized, etc. The steps used, their particular sequence, and the materials involved all contribute to the making of particular devices.
As device sizes have shrunk below 90 nm, one technique known as atomic layer deposition, or ALD, continues to be required for a variety of applications, such as the deposition of barriers for copper interconnects, the creation of tungsten nucleation layers, and the production of highly conducting dielectrics. In the ALD process, two or more precursor gases are delivered in pulses and flow over a wafer surface in a process tool maintained under vacuum. The two or more precursor gases flow in an alternating or sequential manner so that the gases can react with the sites or functional groups on the wafer surface. When all of the available sites are saturated from one of the precursor gases (e.g., gas A), the reaction stops and a purge gas is used to purge the excess precursor molecules from the process tool. The process is repeated, as the next precursor gas (i.e., gas B) flows over the wafer surface. For a process involving two precursor gases, a cycle can be defined as one pulse of precursor A, purge, one pulse of precursor B, and purge. A cycle can include the pulses of additional precursor gases, as well as repeats of a precursor gas, with the use of a purge gas in between successive pulses of precursor gases. This sequence is repeated until a final geometric characteristic, such as thickness, is reached. These sequential, self-limiting surface reactions result in one monolayer of deposited film per cycle.
The delivery of pulses of precursor gases introduced into a process tool can be controlled using a pulse gas delivery (PGD) device (the controlled flow of gas into and out of a delivery chamber using inlet and outlet on/off-type valves simply the timing of the opening of the outlet shutoff valve for a predetermined period of time (pulse) to deliver a desired amount (mass) of precursor gas into the process chamber of the process tool). Alternatively, a mass flow controller (“MFC”), which is a self-contained device comprising a transducer, control valve, and control and signal-processing electronics, has been used to deliver an amount of gas at predetermined and repeatable flow rates, in short time intervals.
Pulse gas delivery (PGD) devices are usually pressure based and optimized to provide repeatable and precise quantities (mass) of gases for use in semiconductor manufacturing processes, such as ALD processes. Typically, as shown in FIG. 1, current PGD devices include a delivery gas chamber 12, an inlet shut off valve 14 for controlling the flow of gas from a gas supply 52 into chamber 12, and an outlet shut off valve 16 for controlling the flow of gas from the delivery chamber 12 to the process tool 54. A host controller or computer 50 runs the gas delivery process as well as carries out all of the control and diagnostic functions for the process tool, including, for example, safety monitoring and control, RF power signals, and other common tasks. Since the volume of the delivery chamber 12 is fixed and known, the amount of gas, measured in moles, introduced into the delivery chamber with each pulse is a function of the gas type, the temperature of the gas in the chamber, and the pressure drop of the gas during the duration of the pulse delivered from the chamber 12. Accordingly, pressure sensor 18 and temperature sensor 20 provide measurements of the pressure and temperature to the controller 24 so that the gas delivered from the chamber during each pulse can be determined. The control logic for running the PGD device has thus been traditionally and typically on the host controller 50 associated with the process tool. Improvements are described in the copending Applications by providing a dedicated controller 24 for separately controlling the pulse delivery process by operation of the inlet and outlet valves 14 and 16.
More recently, certain processes have been developed that require high speed pulsed or time-multiplexed processing. For example, the semiconductor industry is developing advanced, 3-D integrated circuits thru-silicon vias (TSVs) to provide interconnect capability for die-to-die and wafer-to-wafer stacking. Manufacturers are currently considering a wide variety of 3-D integration schemes that present an equally broad range of TSV etch requirements. Plasma etch technology such as the Bosch process, which has been used extensively for deep silicon etching in memory devices and MEMS production, is well suited for TSV creation. The Bosch process, also known as a high speed pulsed or time-multiplexed etching, alternates repeatedly between two modes to achieve nearly vertical structures using SF6 and the deposition of a chemically inert passivation layer using C4F8. Targets for TSV required for commercial success are adequate functionality, low cost, and proven reliability.
These high speed processes require fast response times during the transition time of the pulses in order to better control the processes, making the use of pressure based pulse gas delivery devices problematic. Currently, one approach to increase response time is to use a fast response mass flow controller (MFC) to turn on and off gas flows of the delivery pulse gases delivered to the process tool according to signals received from a host controller. The repeatability and accuracy of pulse delivery using a fast response MFC with a host controller, however, leaves room for improvement, because response times are dependent on the workload of the host controller. The host controller may be prevented from sending timely control signals if it is performing other functions that require its attention. Further, with short duration control signals being sent from the host controller to the mass flow controller, communication jitter can occur causing errors in the delivery of pulses of gas. Workload of the host controller and communication jitter are two sources of error that reduce the repeatability and accuracy of pulse gas delivery when relying to fast communication between the host controller and the mass flow controller delivering pulses of gas.